Mast cells initiate local and systemic immediate hypersensitivity reactions, and also may influence other processes, including innate immunity, inflammation and tissue remodeling. The major component of the secretory granules of all human mast cells on a weight basis is the tryptase family of serine proteases. Two major types, and several subtypes of human mast cell tryptase reside on chromosome 16, including alphaI-alphaII-tryptases and betaI-/betaII-/betaIII tryptase. The sequence homology between types of tryptase is greater than 90 percent, and between subtypes is greater than 98 percent. The current proposal is to continue studies that began with the identification, purification and characterization of this enzyme in 1981, followed by the development of tryptase immunoassays used to assess mast cell involvement in human diseases such as asthma, systemic anaphylaxis and systemic mastocytosis, the biochemical characterization of the enzyme as a heparin-stabilized tetramer resistant to biologic protease inhibitors, the cloning of alpha- and beta-tryptase cDNAs, the elucidation of a novel processing mechanism for beta-protryptase, and the identification of several potential biologic substrates. Four specific aims are now proposed. First, the transcriptional regulation of tryptase genes will be assessed. Second, how different types and subtypes of protryptase are processed will be determined. Third, a novel pH- dependent regulatory mechanism for human tryptase will be explored, and a potential biologic modulator of tryptase investigated. Fourth, the clinical utility of different forms of tryptase (types, subtypes, and maturational states) as markers for mast cell-dependent disease activity will be pursued. Understanding these facets of tryptase gene expression and of how proteolytic activity is regulated will provide a better understanding of the biology and pathobiology of this abundant but mysterious protease, and should facilitate the development of clinically useful agents that affect tryptase activity.